[Arran]

 In actual fact, of all of the tubes out there, the 6L6 is one that is still in production in one form or another, although the envelopes are not the same as the North American made 6L6Gs. The Russian/Soviet 6P3 comes to mind, they have some in a GB style envelope, and some that are in a sort of bulged out GT style, they had a sort of ST version but they looked more European or British. I think that they Chinese are also still making 6L6s, possibly the JJ company in Slovakia, though I would stick with the Russian ones if going for new or NOS.
Regards
Arran